1. Field of the Invention
The present invention relates to a zoom lens system, an interchangeable lens apparatus, and a camera system. In particular, the present invention relates to: a compact and lightweight zoom lens system having a relatively high zooming ratio, less fluctuation in aberrations associated with focusing, excellent optical performance over the entire focusing function, with sufficiently compensated aberrations particularly in close-object in-focus situations, and excellent blur compensation; and an interchangeable lens apparatus and a camera system each employing the zoom lens system.
2. Description of the Background Art
In recent years, interchangeable-lens type digital camera systems (also referred to simply as “camera systems”, hereinafter) have been spreading rapidly. Such interchangeable-lens type digital camera systems can realize: high-quality pictures taken with high-sensitivity; high-speed focusing, and high-speed image processing after a picture is taken; and easy exchange of interchangeable lenses in accordance with the scene to be shot. Furthermore, interchangeable lens apparatuses having a zoom lens system that forms an optical image with variable magnification are popular because they make it possible to vary the focal length freely without the necessity of interchanging lenses.
A compact zoom lens system having a high zooming ratio and excellent optical performance from a wide-angle limit to a telephoto limit has been desired as a zoom lens system to be used in an interchangeable lens apparatus. Various kinds of zoom lens systems having multiple-unit configurations, such as four-unit and five-unit configurations, have been proposed. In such zoom lens systems, focusing can be performed such that some lens units in the lens system are moved in a direction along the optical axis.
For example, Japanese Patent No. 3054185 discloses a zoom lens having a six-unit configuration in which the optical power of the lens units is positive, negative, positive, negative, positive, and positive. With this zoom lens, in zooming from a wide-angle limit to a middle position, magnification is varied using the fourth lens unit with the second lens unit being fixed on the object side, and the sixth lens unit is moved to perform focusing.
Japanese Laid-Open Patent Publication No. 10-111455 discloses a zoom lens having a five-unit configuration in which the optical power of the lens units is positive, negative, positive, negative, and positive. With this zoom lens, the focal length at the wide-angle limit is shorter than the diagonal length of the display. In zooming from a wide-angle limit to a telephoto limit, at least the fifth lens unit is moved to the object side to vary the intervals between the respective lens units. The second lens unit, or a whole or part of a vibration-proof lens unit for optically compensating image blur, is moved along the optical axis to perform focusing.
Japanese Laid-Open Patent Publication No. 2007-279077 discloses a variable magnification optical system having at least four-unit configuration in which the optical power of the lens units is negative, positive, negative, and positive. With this system, in zooming from a wide-angle limit to a telephoto limit, at least the second lens unit and the fourth lens unit are moved to decrease the interval between the first and second lens units, increase the interval between the second and third lens units, and decrease the interval between the third and fourth lens units. In the case of adopting, for example, a five-unit configuration or a six-unit configuration, the fifth lens unit is moved along the optical axis to perform focusing.
In each of the zoom lenses as well as the variable magnification optical system disclosed in the above-described patent documents, since the amount of movement of the lens unit responsible for focusing is determined by the paraxial power configuration in the entire lens system, the amount of fluctuation in aberrations during focusing is not sufficiently compensated from the wide-angle limit to the telephoto limit, and particularly, compensation of various aberrations in a close-object in-focus situation is insufficient. Therefore, neither the zoom lenses nor the variable magnification optical system has excellent optical performance over the entire object distances, from infinite object distance to close object distance. Further, neither the zoom lenses nor the variable magnification optical system disclosed in the patent documents is capable of performing blur compensation, nor has a blur compensation function that satisfies recent requirements for zoom lens systems.